Weight loss drugs and surgery improve body composition in patients with obesity

Both the new weight loss drugs and bariatric (weight loss) surgery improve body composition in patients with obesity by inducing a moderate loss of fat-free mass (including lean muscle) along with a substantial reduction in fat, researchers at Vanderbilt Health have found.

This is important because while a higher percentage of fat mass (FM) is associated with an elevated risk of mortality from obesity-related diseases, including adverse cardiovascular events, a higher percentage of fat-free mass (FFM) is protective against mortality.

More study is needed to determine how FM and FFM change after bariatric surgery or treatment with current GLP-1 receptor agonist drugs in real-world clinical settings, the researchers reported Jan. 9 in the journal JAMA Network Open. 

The study was led by Danxia Yu, PhD, associate professor of Medicine in the Division of Epidemiology, and Jason Samuels, MD, assistant professor of Surgery.

Their retrospective study analyzed the electronic health records of 1,257 patients ages 18 to 65 who underwent bariatric surgery at Vanderbilt Health from 2017 to 2022, and 1,809 patients treated with the drugs semaglutide or tirzepatide from 2018 to 2023.

The study excluded those with a history of end-stage renal disease or congestive heart failure.

Body composition was quantified by bioelectrical impedance analysis, which estimates FM and FFM according to individual characteristics including height, weight, age, race, gender, history of diabetes and GLP-1 treatment duration.

The researchers found that, over 24 months, both medical and surgical weight loss approaches led to significant reductions in FM, modest reductions in FFM, and increases in the FFM/FM ratio, reflecting improved body composition. Male patients showed better long-term preservation of FFM than female patients.

First authors of the paper were graduate student Zicheng Wang, MS, and postdoctoral fellow Lei Wang, PhD, both in Epidemiology.

Other co-authors were Xinmeng Zhang and You Chen, PhD (Biomedical Informatics and Computer Science); Brandon Lowery (Vanderbilt Institute for Clinical and Translational Research); Lauren Lee Shaffer, MS, and Quinn Wells, MD (Cardiovascular Medicine); and Charles Flynn, PhD, Brandon Williams, MD, Matthew Spann, MD, and Gitanjali Srivastava, MD (Surgery).

The study was supported in part by National Institutes of Health grants R01DK126721 and R01CA275864.